This invention relates to internal combustion engines and, more particularly, to the timing of an exhaust valve of an engine to promote efficiency of fuel consumption.
A form of the internal combustion engine, generally used for powering automobiles, operates in accordance with the Otto cycle, and may be referred to herein as a gasoline engine, as distinguished from a diesel engine. The gasoline engine, as well as the diesel engine, employs one or more cylinders, each cylinder having a piston movable along an axis of the cylinder with reciprocating motion, and being connected by a connecting rod to the engine crankshaft for driving the crankshaft with rotary motion. Output power of the engine for the driving of a load is obtained from the rotating crankshaft. In the case wherein the load is a vehicle driven by the engine, the engine crankshaft normally is connected via a transmission with selectable gear ratios to a propeller shaft of the vehicle for imparting rotation to the drive wheels of the vehicle.
In the four-stroke form of the gasoline engine, the movement of a piston in its cylinder is characterized by four strokes, which occur in a repeating sequence, the sequence of the four strokes being: an induction stroke, a compression stroke, a power (or expansion) stroke, and an exhaust stroke. During the induction stroke, the piston moves away from the head of the cylinder to produce a vacuum that draws in a mixture of air and fuel vapors via an intake valve generally located in the head of the cylinder. During the compression stroke, the piston moves towards the cylinder head to compress the air-fuel mixture. Approximately at the beginning of the power stroke, there is ignition of the air-fuel mixture and, during the power stroke, the expanding gases produced by the combustion of the fuel drive the piston away from the cylinder head. During the exhaust stroke, the piston moves towards the cylinder head to drive the exhaust gases out of the cylinder via an exhaust valve generally located in the cylinder head. In the usual construction of such an engine, an intake manifold is provided for bringing air and fuel from a carburetor or fuel-injection assembly to the intake ports of the cylinders, and an exhaust manifold is provided for removal of combustion gases via exhaust ports of the cylinders.
It is useful to compare operation of the gasoline engine with the diesel engine. In the case of the gasoline engine, both fuel and air are present in the cylinder during the compression stroke. The temperature produced in the gases within the cylinder is below the ignition temperature of the air-fuel mixture so as to avoid premature ignition of the air-fuel mixture. Ignition is produced by an electric spark of a spark plug, mounted within the cylinder head. In a modern engine, activation of the spark plug is provided by a computer at an optimum moment, relative to the time of occurrence of the power stroke. In the case of the diesel engine, only the air is present in the cylinder during the compression stroke. The geometry of the piston within the cylinder of the diesel engine differs somewhat from the corresponding geometry of the gasoline engine such that the compression stroke of the diesel engine provides significantly more compression of the gases within the cylinder (a compression ratio of approximately 15:1 to 20:1) than occurs in the gasoline engine (a compression ratio of approximately 8:1 to 10:1). As a result, in the diesel engine, the temperature of the air is raised by the compression stroke to a temperature high enough to ignite the fuel. Accordingly, in the diesel engine, the fuel is injected into the cylinder at approximately the beginning of the power stroke, and is ignited by the high air temperature.
It is observed furthermore, that in the usual construction of a gasoline engine and of a diesel engine, the ratio of the expansion of the volume of cylinder gases in the power stroke, namely the final volume divided by initial volume, is equal to the ratio of the compression of the volume of the cylinder gases in the compression stroke, namely the initial volume divided by final volume. The expansion of the cylinder gases in the power stroke is accompanied by a reduction in the temperature of the cylinder gases. Well-known theoretical considerations show that an important consideration in determining the efficiency of the engine is the ratio of the gas temperature at the beginning of the power stroke to the gas temperature at the end of the power stroke.
In spite of the foregoing theoretical considerations for the efficiency of a power stroke of the engine, there appears to be other factors in the operation of an engine that result in a needless wasting of the energy in the fuel with a resultant reduction in the fuel efficiency of the engine. In a test conducted by the present inventor in warm weather, an automobile powered by a gasoline engine was driven under speed control on the highway over a period of time, such as one minute, at an engine speed of 3000 RPM (revolutions per minute) corresponding to approximately 60 mph (miles per hour). The test was then conducted again by driving the automobile under a resumed speed control in the opposite direction of the highway so as to cancel out effects of any hills and the presence of any winds. The average amount of the fuel consumed was determined, which amount for illustrative purposes may be considered to be 200 cc (cubic centimeters). The vehicle was parked and the transmission put into “Park” gear, and the engine was “raced” with no load at the same engine speed of the highway driving at 3000 RPM. Again, the fuel consumption over the foregoing testing interval of one minute was measured, and determined to be 150 cc, only 25 percent less than the amount of fuel consumed under loading, namely the foregoing amount of 200 cc. The difference of only 25 percent shows that the major source of consumed fuel lies directly within the operation of the engine. Therefore there is a need for obtaining better fuel economy from an engine, and in view of the foregoing testing, it appears to be necessary to alter the engine itself in order to obtain improved fuel economy.